1. Field of the Invention
The present invention relates to a blade for an electrophotographic apparatus which is an image forming apparatus using an electrophotographic process such as an electrophotographic copier, a laser beam printer and a facsimile, and to a developer amount controlling blade. The present invention also relates to a mold which can be used for molding the blade for the electrophotographic apparatus.
2. Description of the Related Art
Generally, an electrophotographic apparatus uses a cleaning blade for removing toner remaining on a photosensitive member after the photosensitive member has transferred an image onto a recording paper, and a developer amount controlling blade so as to form a thin layer while triboelectrically charging a developer in a development apparatus and the like.
Such a blade for an electrophotographic apparatus is generally formed of a rubber sheet, a metallic thin sheet, a resin sheet and a laminate of them. The cleaning blade is made of a blade member which abuts on the photosensitive member and a supporting member for supporting the blade member into a predetermined position. The developer amount controlling blade is made of a blade member which is pressure-welded with a developer bearing member and the supporting member for supporting the blade member into the predetermined position. A surface which is pressure-welded with the developer bearing member of the blade member has a function of controlling a friction charge of the developer, and accordingly is referred to as a charge-controlling surface. A surface layer of the charge-controlling surface can be referred to as a charge-controlling layer.
Such a blade member used as the electrophotographic apparatus employs, for instance, a plate material such as a urethane resin, a polyamide elastomer or a silicone rubber. In particular, blade members of the cleaning blade and the developer amount controlling blade are required to have a high accuracy of a dimension; and furthermore both of the blade members often use a highly abrasion-resistant material and use a polyurethane resin in many cases, because of performing the function when sliding on a rotating member.
In recent years, an electrophotographic process has a trend of forming an image of higher quality at a higher speed, and both a cleaning blade and a developer amount controlling blade are required to show higher performance. In particular, the developer amount controlling blade is required to make a developer thinly and uniformly carried on the surface of a developer bearing member in a state that the developer has a uniform charged amount, it is known that surface properties of a blade member greatly affect on a transportation force and the charged amount of the developer.
Conventionally, it has been thought that the smoother the charge-controlling surface of the developer amount controlling blade is made, the more uniform the developer particles are charged and transported. However, as a result of having recently studied an effect of the flatness of the charge-controlling surface on a uniform charge and transportation of the developer in detail, it was found that it was rather better to roughen the developer-controlling surface to some extent, in order to uniformly electrify and transport the developer. Accordingly, the surface of the blade member can be stably roughened.
In the case of the cleaning blade as well, the blade member is required to have a dimension of high accuracy, because the blade member must completely remove a developer remaining on a photosensitive member, which has recently a small diameter. It is also important for the cleaning blade to have an edge face with precise surface roughness (edge accuracy), which contacts the photosensitive member. When the surface roughness accuracy is 10 μm or more, the cleaning blade causes poor cleaning and occasionally results in causing a line on a recording paper. For this reason, the surface properties of a part contacting a die surface also become important.
In order to stably and inexpensively produce a blade of higher accuracy for an electrophotographic apparatus, with respect to such an accuracy of a dimension and surface properties, a mold is important. A mold is expected which can maintain adequate peelability and demolding properties for a long period of time when repeatedly molding the blade, in order to inexpensively manufacture the blade for the electrophotographic apparatus having superior dimensional accuracy and surface properties.
Japanese Patent Application Laid-Open No. 2001-305858 describes a manufacturing method which has a superior thickness accuracy, does not need to subject a die to an accurate working and does not need to clean a sheet after having molded the sheet. A technology disclosed in Japanese Patent Application Laid-Open No. 2001-305858 includes pouring a solventless two-component liquid silicone rubber into the inside of a die having a cylindrical shape by using a centrifuge molding method to form a molded body of the silicone rubber, and then pouring a material of the blade for the electrophotographic apparatus therein to cure the material. Hereby, the technology is assumed to show an effect of controlling the thickness accuracy to 0.1 mm or less. However, the method may cause problems of making the silicone rubber deformed, torn and hardly demolded due to the volatilization of a volatile component, when the molding and demolding operation is repeated for a long period of time.
Japanese Patent Application Laid-Open No. 2003-231142 proposes a method of forming a releasing layer which is made from a resin having a polysilazane-based or polysiloxane-based chain as a main chain, and has a hardness in a range of 55 to 85 degrees by a JISA type, in the inside of a die, as a method which can maintain mold-releasability for a long period of time without cleaning a release agent after molding. However, the method occasionally has a problem in stability after the reaction. While the die is used for molding for a long period of time, a chemical reaction occurs between the materials of the surface of the releasing layer and of a blade member, which may make the releasing layer hardly maintain mold-releasability. Silica which remains in silicone rubber as a reactive group even after the silicone rubber has been cured by a reaction reacts with the material of the blade member, and may make the releasing layer not maintain adequate mold-releasability for a long period of time.